The present invention is directed to a system and method for calibrating a differential steering system. More particularly, the present invention is directed to a system and method for calibrating a hydraulically driven differential steering system.
Differential steering systems are commonly used in many types of vehicles, including, for example, those vehicles designed for agricultural and construction related activities. Each of these vehicles typically includes at least two ground engaging traction devices, which may be, for example, continuous belts, tracks, or tires. The ground engaging traction devices are disposed on opposites sides of the vehicle and may be rotated to propel the vehicle along a chosen path.
A differential steering system guides the vehicle along a chosen path by changing the relative velocity of the ground engaging traction devices. For example, to turn the vehicle to the left, the left ground engaging traction device is rotated at a slower velocity than the right ground engaging traction device. To turn the vehicle to the right, the right ground engaging traction device is rotated at a slower velocity than the left ground engaging traction device. The relative difference in velocities causes the vehicle to turn in the direction of the slower ground engaging traction device. The rate of turn, or turning radius, may be adjusted by increasing or decreasing the magnitude of difference in velocities between the ground engaging traction devices. Increasing the magnitude of difference in velocities results in a tighter turn, or a decreased turning radius. Decreasing the magnitude of difference in velocities results in a wider turn, or an increased turning radius.
Some differential steering systems include a hydraulic system that has a pump and a fluid motor. The pump drives the fluid motor to rotate a shaft in one of two directions. Rotation of the shaft in one direction causes one ground engaging traction device to rotate at a higher velocity than the other ground engaging traction device. Rotation of the shaft in the second direction causes the other ground engaging traction device to rotate at a higher velocity. The rotational velocity of the shaft dictates the magnitude of the velocity difference between the ground engaging traction devices.
These hydraulically driven differential steering systems may include a series of electrical, mechanical, and hydraulic components that work together to rotate the output shaft at a desired speed and direction. These components are, however, subject to manufacturing differences and not all components will behave in an identical manner. Accordingly, once a particular differential system is assembled, the system may need to be calibrated to account for performance differences in the components. In addition, the system may need to be calibrated after undergoing maintenance or repair and after the vehicle has been operated for a given number of hours.
The calibration procedure typically produces a calibration map or calibration function for the particular steering system that may be stored in the memory of a control system. The calibration map is a set of data points that account for any operating discrepancies in the system components. These data points may be used by the control system to scale a command signal sent to the steering system to compensate for factors such as manufacturing differences in the system components. The scaling of the command signal helps ensure that the output of the steering system matches the desired output so that the desired turning radius is achieved. One exemplary system for calibrating a hydraulic control and determining a set of calibration data points is described in U.S. Pat. No. 5,762,475.
Typically, the calibration procedure for a differential steering system involves connecting an external control to the vehicle and operating the vehicle through a series of test conditions. The external control monitors the operation of the steering system as the vehicle performs the test conditions and develops the data points necessary to create the calibration map. The calibration map may then be stored in the control system for use during standard operation of the vehicle.
This type of calibration procedure, however, can be time consuming and inconvenient. As an external control may need to be connected to the vehicle, a skilled technician may be required to perform the calibration procedure. This will require that the vehicle has to be transported to a maintenance facility or that the skilled technician visit the vehicle. This may result in down time for the vehicle as it waits for the calibration to be performed. Once the external control is connected, the external control may need to be monitored while the vehicle is operated. This may require that two people be present on the vehicle during the calibration process, one to operate the vehicle and one to monitor the external control.
The calibration system and method of the present invention solves one or more of the problems set forth above.
One aspect of the present invention is directed to a method of calibrating a differential steering system in a vehicle. An initiation signal is received. At least one operating condition of the vehicle is monitored. A variable activation signal is applied to an actuation device operable to initiate a flow of pressurized fluid to a steering motor when the at least one operating condition is within a predetermined range. The rotation of the steering motor is monitored. A data point indicative of the value of the variable activation signal applied to the actuation device is captured when the steering motor begins to rotate in response to energization of the actuation device.
In another aspect, the present invention is directed to a differential steering system. The differential steering system includes a source of pressurized fluid operable to selectively generate a first flow of pressurized fluid in a first direction and a second flow of pressurized fluid in a second direction. A steering motor is in fluid connection with the source of pressurized fluid and is configured to rotate a shaft in one direction when the flow of pressurized fluid is in the first direction and to rotate the shaft in an opposite direction when the flow of pressurized fluid is in the second direction. An actuation device is connected to the source of pressurized fluid and is configured to selectively initiate the first flow of pressurized fluid in the first direction and the second flow of pressurized fluid in the second direction. A control is configured to apply a variable activation signal to the actuation device to initiate one of the first and second flows of pressurized fluid and to capture a data point indicative of the current at which the steering motor begins to rotate the shaft.